10 November 2010

Universally Speaking

From a distance, a television screen image looks so smooth and nice. But a closer look would reveal that it consists of a large collection of tiny discrete pixels. Our universe is also like that. At a high level, i.e., close to our everyday experiences level, everything seems to be smooth and reasonably predictable. But at a deep low level, i.e., atomic level, everything comes in discrete quantities and tiny discrete entities. These tiny discrete entities are known as elementary particles and they are the building blocks of our universe. At this level, our universe is so bizarre that we needed a new kind of physics known as quantum mechanics to describe the elementary particles behavior and their interactions with each other. An elementary particle can occupy more than one location at a time. Time goes in both directions. An elementary particle can only be predicted (its location and momentum) in probabilistic terms. This probabilistic nature is the fundamental reality of nature and is nothing to do with our lack of understanding! At a high level, in our everyday experiences, we see their collective averaged-out and smoothed-out behavior and hence the predictable reality of nature. Quantum mechanics is one of the best theory humans ever conceived and it has been accurately verified so many times again and again! Quantum mechanics neatly describes the atomic structure and all the elements in the periodic table!

The image below shows all the known elementary particles. Each elementary particle symbol is mentioned in the middle and its mass, charge, spin and name are mentioned from top to down as indicated in Up quark.

First three columns show the matter particles (also known as fermions) and they come in three generations. Each generation of particles are same (all other properties are same) except II-generation is heavier (look at the mass value in the picture) than I-generation, and III-generation is heavier than II-generation. As II and III generation of particles immediately decay into lowest energy level, i.e., I-generation particles, we only see matter made of I-generation particles (but II and III generation of particles can be produced in the laboratory). The matter particles are also grouped as quarks and leptons.

Fourth column shows the force carrier particles (also known as bosons) and they are responsible for the fundamental forces of nature. In other words, exchanges or mediations or interactions of these particles result as forces. There are four known fundamental forces in nature: electromagnetism (photon), gravity (graviton), strong (gluon) and weak (W and Z) nuclear forces. Photons are responsible for electric field, magnetic field and light (electromagnetic wave). Gluons are responsible strong nuclear force – the force that binds protons together inside the atom. W and Z particles are responsible for weak nuclear force that is associated with radioactivity. Gravitons (not yet detected; and that is why it is not shown in the image) are responsible for gravity.

Every particle has its associated antiparticle as well (antiparticles were first theoretically predicted and later found to be true). For example, electron's antiparticle is positron. Antiparticles are not shown in the image here. New particles are created along with their associated antiparticles (this is what happens when we create them in the laboratory). When a particle and its antiparticle collide, both can be annihilated and other particles such as photons produced. But our known universe consists of only particles.

The image below shows how the elementary particles interact with each other.

The top part shows the matter particles: leptons and quarks. The middle part shows the force particles: Photon, W and Z, and gluon. The bottom part shows theoretically predicted and not yet detected force particle known as Higgs boson.

Gluons only interact with quarks. They bind quarks together to form atomic nuclei.

Photons interact with matter particles.

Higgs boson interacts with particles that have mass (photon and gluon do not have mass); perhaps mass results from particles interacting with Higgs field (Higgs field created by Higgs bosons; like magnetic field created by photons).

The image below describes our known universe based on these elementary particles.

The left side shows the unification of matters. 2 up quarks (charge 2/3) and 1 down quark (charge -1/3) form a proton (2/3+2/3-1/3 = 1) with unit (1) of positive charge. 1 up quark and 2 down quark form a neutron (2/3-1/3-1/3 = 0) with neutral (0) charge. Protons and neutrons form atomic nuclei. And the electrons around the nuclei form atoms. Atoms combine together create molecules. Stars, black holes, planets, living things including people are made up of atoms and molecules.

The right side shows the unification of forces. Gluon interactions are explained by quantum chromo-dynamics. Electromagnetism is explained by quantum electro-dynamics. Electromagnetism and nuclear weak force can be unified with a single theory, electro-weak theory. Electro-weak theory and chromo-dynamics can be unified with a single theory, grand unified theory. The final idea is to combine the grand unified theory with gravity and form a single theory – theory of everything! But this theory still eludes us.

In classical mechanics, Newton first described gravity and later Einstein further corrected it by including relativistic principles – general relativity. Gravity is the weakest force (far far weaker than weak nuclear force). Though the entire earth pulls an iron metal down, a small magnet is sufficient enough to pull it up! As gravity is so weak, we don't realize it between everyday objects and people. It needs huge objects like the earth to notice its influence. Though it is so weak, this is the force that keeps us on the earth, keeps the moon goes around the earth, keeps all planets rotates around the sun, keeps stars to form a galaxy and galaxies to form clusters, etc. Though the general relativity describes gravity accurately, it fails to describe anything at quantum level. Quantum nature of gravity (and hence theory of everything) is needed to fully describe black holes and the big-bang.

Einstein's equation E = mc^2 describes how mass and energy are related. In stars, some atomic mass is converted into energy (in the form of other elementary particles such as photons – electromagnetic radiation). This is how nuclear power stations and atomic bombs work. Likewise, new elementary particles can also be produced from energy. In the particle accelerators such as the Large Hadron Collider (LHC), particles such as protons are accelerated at very high speed and smashed into each other to create new particles. These experiments help us to find theoretically predicted particles such as Higgs boson (producing gravitons requires far-far more energy than what our current particle accelerators are capable of) and totally new particles, and ultimately get a glimpse of the secret of nature!

Though we only have some vague hypothesis (from String theories and their extension M-theory, etc.) about how the big-bang might have originated, we have many reasons and evidences for the big-bang. The big-bang occurred 13.7 billion years ago and it is the beginning of everything in our known universe, even space and (arrow of) time as we know! As time goes in both directions at the fundamental level, there is no before, before the big-bang in the usual sense. Also, as per the general relativity, it is senseless to ask what is before the big-bang (it is like asking what is south of the South Pole). The big-bang created a very low entropy (i.e. a concentrated energy or very high order) and since then as per entropy principle (second law of thermodynamics: disorder tends to increase – and ultimately reach total disorder or equilibrium) the entropy of our universe has been increasing. Though the disorder of our universe has been continuously increasing, some orders (because of fundamental natural forces) have temporarily been created from existing high energy, such as galaxies, stars, planets and life. As we exist in the aftermath of low entropy event, the big-bang, and as entropy goes from low to high, we perceive time goes in one direction, from past to present to future – arrow of time (It is like sensing up and down on the earth because of its high gravitational influence, when actually there is no up and down in the universe. Likewise we sense an arrow of time in the aftermath of low entropy event). As our universe approaches very high entropy, i.e. total disorder or equilibrium, there will not be any sense of arrow of time – no before or after! (our universe is approximately half way through to that point).

As we create elementary particles in the particle accelerators, the big-bang created all the elementary particles of our universe (along with antiparticles; but not so fully understood reason, they are missing from our known universe). As our universe expanded and cooled, these elementary particles interacted with each other and combined together and formed the universe as we observe.

Any object closer to a heavy object rotates faster than far away object. For example, the venus rotates the sun faster than the earth, and the earth rotates faster than the mars and so on. If the earth rotates slower than the sun's gravitational pull, it will be sucked into the sun, and if it rotates way faster than the sun's gravitational pull, it will go out of the solar system. So, objects closer to a heavy object rotate faster than further away objects. This logic applies to galaxies as well. Astronomers observed stars speed as they rotate around the center of galaxies (at the center lies a heavy dense object known as block hole). They are surprised to find that the stars in the outer edge of the galaxy rotate as fast as stars closer to the center. The stars rotate around the galaxies as if there are far more matter than what we observe (another possibility is that our understanding of gravity is wrong at very large scale, but in many respect it does not seem to be the case). This hidden matter is known as dark matter – some unknown elementary particles. Dark matter may not interact with ordinary matter via electromagnetic forces except through gravitational influence.

The big-bang theory and the general relativity predict expansion of our universe (expansion of space itself). Because of gravitational pull of the matter in the universe, we thought the universe would expand slower and slower rate. Later astronomers observed that the universe actually expands at an increasing rate (faster and faster), as if some hidden energy pushing them away. This hidden energy is known as dark energy. It may be considered as a vacuum energy. It is known to be very homogeneous, not very dense and is not known to interact through any of the fundamental forces other than gravity. Dark energy can only have such a profound impact on the universe, making up 74% of universal density, because it uniformly fills otherwise empty space.

Though we have discovered two most successfully verified theories: the general relativity (at high level) and quantum mechanics (at low level), still there are many mysteries. What exactly is caused the big-bang to happen? What are the conditions before (in whatever sensible sense) the big-bang? Why are more particles in the universe than antiparticles? What is dark matter? What is dark energy? Perhaps the deepest mystery of all is why there exists something instead of nothing! Perhaps many of these mysteries can be explained when we have the theory of everything. Though there are many mysteries that need to be explained, none of it is about life or our everyday experiences!